Separation of oxygen, nitrogen, and argon from air



'0a.4, 1932. F. POLLmER Em. `1,880,981

SEPARATION OF OXYGEN, NITROGEN, AND ARGON FROM AIR Filed July 3, 1930Patented Oct. 4, A1932 isaiasi UNITED erlfiasl PATENT.; OFFICE FRANZIPOLLITZER, F GROSSHESSELOHE, NEAR MUNICH, AND STEPHAN STARK,

' GRUNWALD, NEAR MUNICH, GERMANY SEPARATION 0F OXYGEN, NITRUGEN, ANDAEGON FROM AIB Application filed July 3, 1930, Serial No. 465,772, andin Germany February 8, 1930.

The invention relates to a process for obtaining oxygen and nitrogen bya two-stage rectification of liquid air with the simultaneous productionof` argon in a third rectifying column.

For the separation of argon from the air, the maj orportion of thenitrogen is first separated and the residue consisting principally ofoxygen and argon is separated into pure oxygen and a mixture rich inargon by a further rectification. The heat-interchange necessary foreffecting the latter rectification is obtainedv by means of a cycleeither of nitrogen, with indirect heating or cooling of the column, orof argon, with direct exchange.

The present invention makes possible a considerable simplification andreduction of expense in the production of argon in connection with thetwo-stage rectification of air. In the first stage nitrogen is obtainedunder a pressure which is sufficient to permit its condensation in theoxygen-rich liquid in the lower part of the argon rectification column.In the process of the invention a portion of the nitrogen is withdrawnfrom the first column in the gaseous state and utilized for heating andcooling the argon column. I-Iitherto this nitrogen, insofar as it wasnot returned in the liquid state to the first rectification column, wasutilized for washing oxygen out of the nitrogen vapors in the secondrectification column, and as much nitrogen as was available was used forthis purpose in order to make the washing operation as complete aspossible. The withdrawal of nitrogen for use in the argon column hasheretofore been considered to be incompatible with the obtaining of ahigh yield of oxygen or the production of a practically pure nitrogen.

In the process of the invention a part of the oxygen-rich mixture isreworked in the argon column. At the same time the first column isoperated to produce a fraction containing a high percentage of nitrogen,and in lthe second column the rectification is improved by increasingthe plate number or effeet.. It was found that the withdrawal of argonfromthesecond column promotes the separation of oxygen and nitrogen, andcomensates the unfavorable effect of diminishing the amount of washingliquid.

By way of illustration, one method of carrying out the invention will bedescribed with reference to the accompanying schematic drawing.

In the drawing, l and 2 are 4the two rectifying columns of a two-stagerectifier, such as is commonly used for the production of oxygen andnitrogen. 3 is the argon rectification column, the argon-oxygen mixturebeing introduced through pipe 4. The pressure column l contains asufficient number of plates that nitrogen containing 1% or less ofoxygen is obtained at the upper end. The second column is made so largethat it has the effect of fifteen ideal rectification plates. In thisway the nitrogen vapor may be purified to a content of oxygen of about2%. ,0

For heating the argon column a part. of the nitrogen is withdrawn in thegaseous state from the nitrogen condenser 5 or below it, at the pressureof about five atmospheres existing in column l and is liquefied in coil6 of the argon vaporizer 7.y The liquid nitrogen is then expandedthrough valve 8 into condenser 9 as a cooling means for the condenser.The vaporized nitrogen leaving lat 10 can be conducted, together withthe nitrogen leav-,BO ing the second column at 1l, to a counter currentheat exchanger (not shown).

In the method of operation herein described only a part of the oxygenobtained in column 2, for example one-half, is introduced into the argonrectifying column 3. If column 2 is operated to produce an oxygen ofover 99% in purity, as is demanded by present industrial requirements,very little argon would be obtained by the further working of thisoxygen. Therefore, in the process of the invention the oxygen to betreated in the argon column is withdrawn from a higher portion of column2 where the oxygen content of the liquid is between 90 and 98%. g5 Inthe lower part of column 3 this oxygen is brought to the same or ahigher purity as that produced in column 2. The lower parts of the twocolumns therefore operate in parallel with reference to the liquid. Withthis 100 method of operation it is possible to withdraw at 12 asubstantial proportion of the argon content of the air, in the form ofaV mixture containing 50% to 90% of ar on.

v A Thus the process of the invention aior s a.

simple method of simultaneously obtaining from the airy practically pureoxygen, nitrogen and argon.

In the same way the process is generally 1o applicable to the separatlonof ternag mixtures, where the ar on is represente by a gas ofintermediate oiling point,

' We claim:

A-process for the production of argon, oxy- 15 gen and nitrogen by thelow temperature rectification of air which comprises subjecting liquidair to two stages of rectification, operating the first stage to producea fraction containing a high percentage of nitrogen, withdrawing only aportion of the oxygenargon mixture in liquid form from the secondrectification stage at a point where the oxygen content of the liquid isabout 90 to 98%, lntroducing said oxygen-argon mixture into the middleportion of a further rectification column, and subjecting saidoxygen-argon mixture to further rectification, the mixture being heatedby the liquefaction of a portion ofthe gaseous nitrogen fraction fromthe lirst stage and being cooled by the evaporation of the nitrogen thusliquefied, high percentage oxygen being obtained at the bottom of saidfurther rectification column.

In testimony whereof, We ax our signatures.

FRANZ POLLITZER. STEPHAN STARK.

